Piston rod and free piston engine

ABSTRACT

An internal combustion engine may include an engine block, a cylinder defining at least one combustion chamber, and a piston in the cylinder. The piston may travel in a first stroke from one end to an opposite end of the cylinder, and may be sized relative to the cylinder to enable an expansion stroke portion of the first stroke while the piston travels under gas expansion pressure, and a momentum stroke portion of the first stroke for the remainder of the first stroke following the expansion stroke portion. A passageway may be formed in the piston rod to communicate gas flow between a first combustion chamber and an area external to the cylinder when the piston is in a first position, and to communicate gas flow between a second combustion chamber and an area external to the cylinder when the piston is in a second position.

TECHNICAL FIELD

The present disclosure relates to the field of internal combustionengines, and more particularly to the field of internal combustionengines having a free piston.

BACKGROUND

Internal combustion engines are known. The most common types of pistonengines are two-stroke engines and four-stroke engines. These types ofengines include a relatively large number of parts, and require numerousauxiliary systems, e.g., lubricant systems, cooling systems, intake andexhaust valve control systems, and the like, for proper functioning.

SUMMARY

Some embodiments may relate to a linear reciprocating engine. The linearreciprocating engine may include an internal combustion engine. Theinternal combustion engine may include a cylinder having a firstcombustion chamber at a first end thereof and a second combustionchamber at an opposing second end thereof, a piston slidably mountedwithin the cylinder, and a piston rod having a passageway extendingthrough the piston into both combustion chambers. There may be providedat least one first opening in a first side of the piston rod configuredto move into and out of the first combustion chamber to selectivelycommunicate gas to the first combustion chamber, and at least one secondopening in a second side of the piston rod configured to move into andout of the second combustion chamber to selectively communicate gas tothe second combustion chamber. The piston may be slidable between afirst position where the first opening is outside the first combustionchamber and the second opening is inside the second combustion chamber,and a second position where the first opening is inside the firstcombustion chamber and the second opening is outside the secondcombustion chamber.

According to some embodiments, an engine may be provided that enablesgas to be communicated to each of two combustion chambers at separatetimes. Gas may be constantly supplied to flow through the passageway inthe piston rod, while the gas is allowed to enter the cylinder only whenan opening among the first openings and second opening is incommunication with the cylinder. The first opening may include one ormore openings, and the second opening may include one or more openings.Gas may travel through the piston rod to supply both of the combustionchambers appropriately during the various phases of the stroke of theengine.

Exemplary advantages and effects of the present invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings wherein certain embodiments are set forth by wayof illustration and example. The examples described herein are just afew exemplary aspects of the disclosure. It is to be understood thatboth the foregoing general description and the following detaileddescription are exemplary and explanatory only and are not restrictiveof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a free piston engine, in accordance withembodiments of the present disclosure;

FIG. 2 is a perspective partial cross-sectional view of the engine ofFIG. 1 with the piston at top dead center on a right side of thecylinder, in accordance with embodiments of the present disclosure;

FIG. 3 is a perspective cross-sectional view of the engine of FIG. 1, inaccordance with embodiments of the present disclosure;

FIGS. 4A-4C are views of a piston kit, in accordance with embodiments ofthe present disclosure;

FIG. 5 is a cross-sectional view of the engine of FIG. 1 with the pistonat top dead center on the right side of the cylinder, in accordance withembodiments of the present disclosure;

FIG. 6 is a cross-sectional view of the engine of FIG. 1 with the pistonin an expansion portion of a stroke from the right side of the cylinderto a left side of the cylinder, in accordance with embodiments of thepresent disclosure;

FIG. 7 is a cross-sectional view of the engine of FIG. 1 with the pistonat the end of the expansion portion of the stroke from the right side ofthe cylinder to the left side of the cylinder, in accordance withembodiments of the present disclosure;

FIG. 8 is a cross-sectional view of the engine of FIG. 1 with the pistonin a momentum portion of the stroke, in an early stage of compressinggasses on the left side of the cylinder, in accordance with embodimentsof the present disclosure;

FIG. 9 is a cross-sectional view of the engine of FIG. 1 as compressioncontinues on the left side of the cylinder beyond the compressionillustrated in FIG. 8, in accordance with embodiments of the presentdisclosure;

FIG. 10 is a cross-sectional view of the engine of FIG. 1 with thepiston at top dead center on left side of the cylinder, in accordancewith embodiments of the present disclosure;

FIG. 11 is a cross-sectional view of the engine of FIG. 1 with thepiston in an expansion portion of a stroke from the left side of thecylinder to the right side of the cylinder, in accordance withembodiments of the present disclosure;

FIG. 12 is a cross-sectional view of the engine of FIG. 1 with thepiston at the end of the expansion portion of the stroke from the leftside of the cylinder to the right side of the cylinder, in accordancewith embodiments of the present disclosure;

FIG. 13 is a cross-sectional view of the engine of FIG. 1 in a momentumportion of the stroke, in an early stage of compressing gasses on theright side of the cylinder, in accordance with embodiments of thepresent disclosure;

FIG. 14 is a cross-sectional view of the engine of FIG. 1 as compressioncontinues on the right side of the cylinder beyond the compressionillustrated in FIG. 13, in accordance with embodiments of the presentdisclosure; and

FIG. 15 is a cross-sectional view of an engine with the piston at topdead center on the left side of the cylinder, in accordance withembodiments of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates to internal combustion engines. While thepresent disclosure provides examples of free piston engines, it shouldbe noted that aspects of the disclosure in their broadest sense, are notlimited to a free piston engine. Rather, it is contemplated that theforgoing principles may be applied to other internal combustion enginesas well.

As used herein, unless specifically stated otherwise, the term “or”encompasses all possible combinations, except where infeasible. Forexample, if it is stated that a component includes A or B, then, unlessspecifically stated otherwise or infeasible, the component may includeA, or B, or A and B. As a second example, if it is stated that acomponent includes A, B, or C, then, unless specifically statedotherwise or infeasible, the component may include A, or B, or C, or Aand B, or A and C, or B and C, or A and B and C.

An internal combustion engine in accordance with the present disclosuremay include an engine block. The term “engine block,” also usedsynonymously with the term “cylinder block,” may include an integratedstructure that includes at least one cylinder housing a piston. In thecase of a free piston engine block, the engine block may include asingle cylinder, or it may include multiple cylinders.

In accordance with the present disclosure, a cylinder may define atleast one combustion chamber in the engine block. In some internalcombustion engines in accordance with the present disclosure, acombustion chamber may be located on a single side of a cylinder withinan engine block. In some internal combustion engines in accordance withthe present disclosure, the internal combustion engine may include twocombustion chambers, one on each side of a cylinder within an engineblock.

Embodiments of the present disclosure may further include a piston inthe cylinder. In accordance with some embodiments of the disclosure usedin a free piston engine, the piston may include two heads on oppositesides. In some embodiments, the piston may be considered to be “slidablymounted” in the cylinder. This refers to the fact that the piston mayslide through a plurality of positions in the cylinder from one side ofthe cylinder to the other. While the present disclosure describes pistonexamples, the invention in its broadest sense is not limited to aparticular piston configuration or construction.

FIG. 1 illustrates an exemplary embodiment of a free piston engine 10according to the present disclosure. Free piston engine 10, which issometimes referred to herein simply as an engine, is one example of aninternal combustion engine. Free piston engine 10 includes an engineblock 8. A cylinder 12 defining at least one combustion chamber may beincluded in engine block 8 and may have a central, longitudinal axis A,and, as shown in FIG. 2, a double-faced piston 50 mounted in cylinder12. Piston 50 may be configured to travel in a first stroke from a firstend of the cylinder to an opposite second end of the cylinder, and in asecond stroke from the second end of the cylinder back to the first endof the cylinder. FIG. 2 illustrates a cutaway view showing a perspectivepartial cross-sectional view of the engine of FIG. 1. FIG. 3 illustratesa perspective cross-sectional view, including a cross-sectional view ofpiston 50. FIGS. 5-10 illustrate an exemplary movement of piston 50 froma first end of the cylinder to a second end of the cylinder. At leastone piston rod portion may be connected to the piston rod and may extendfrom a location within the at least one combustion chamber to an areaexternal to the cylinder. As used herein, the term “piston rod portion”includes any portion of a rod or shaft, extending from a piston. In someembodiments, a piston rod portion may be a portion of a monolithicstructure that makes up the piston, as well as other components. In someembodiments, a piston rod portion may be a portion of a piston rod thatextends from only one face of a piston.

By way of example, as shown in FIGS. 2 and 3, a piston rod 40 mayinclude a first piston rod portion 42 and a second piston rod portion43. First piston rod portion 42 may extend from one face of piston 50.First piston rod portion 42 may extend from a location within the atleast one combustion chamber to an area 65 external to the cylinder.Similarly, second piston rod portion 43 may extend from an opposite faceof piston 50, to another area 67 external to cylinder 12. A piston kitmay include first piston rod portion 42, second piston rod portion 43,and piston 50. Piston rod portions 42 and 43 may be monolithic with eachother, or may be completely separate structures, each extending from anopposite side or face of piston 50. For example, piston kit 56 may beformed from a single piece of material. Piston rod 40 may be monolithicwith piston 50. In some embodiments, first piston rod portion 42 andsecond piston rod portion 43 may be monolithic with each other whilebeing separate from piston 50.

Cylinder 12 may include a first combustion chamber 71 and a secondcombustion chamber 73 (see FIG. 7). Piston 50 may be configured to slidealong axis A. In various positions within cylinder 12, there may be afluid communication path that connects first combustion chamber 71 withan air supply, or that connects second combustion chamber 73 with an airsupply.

Reference is now made to FIG. 5, which illustrates a sidecross-sectional view of engine 10. An area external to cylinder 12(e.g., areas 65 and 67) may include a vestibule at each end of thecylinder that may be a space configured for supplying gas, such as air,to each of the combustion chambers at the opposite ends of the cylinderfrom one or more sources of the gases external to the cylinder. Forexample, FIG. 5 shows a first vestibule 30 and a second vestibule 31.First vestibule 30 is exterior to cylinder 12 and thus exterior to firstcombustion chamber 71, and second vestibule 31 is exterior to cylinder12 and thus exterior to second combustion chamber 73. The vestibules maybe contained by a portion of the structure forming engine block 8 or maybe formed by a separate structure connected to engine block 8. Thevestibules may be connected to an inlet manifold (not shown) thatsupplies gas. A passageway 46 that may be a part of piston rod 40 may beconfigured to deliver gas from first vestibule 30 to cylinder 12,including first combustion chamber 71. In some embodiments, passageway46 may be configured to deliver gas from second vestibule 31 to cylinder12, including second combustion chamber 73.

Cylinder 12 may include a peripheral cylinder wall 13 and exhaust ports18 in peripheral cylinder wall 13. In some embodiments, exhaust ports 18may consist of a single port. Exhaust ports 18 may be connected to anexhaust manifold configured for receiving exhaust gases or other gasesfrom the combustion chambers and directing the gases away from thecylinder for exhaust aftertreatment. In the manner discussed above, forexample, a passageway of the piston rod may be configured to introducegas into a combustion chamber from a location outside the cylinder.Also, gases may exit the cylinder through an exhaust port, such asexhaust ports 18. In an embodiment, areas 65 and 67 external to cylinder12 may simply refer to any region on an opposite side of a cylinder head14, 15 from cylinder 12, regardless of whether the region is in directcontact with a cylinder head. In some embodiments, other ports may beprovided to introduce gases from a manifold or other source locatedalongside the cylinder, rather than at ends of the cylinder. Thus, in ageneral sense, locations outside the cylinder may be at the ends of thecylinder, alongside the cylinder, or a combination of both, for example.

In accordance with embodiments of the disclosure, a piston rod mayinclude a passageway configured to communicate gas flow between at leastone combustion chamber and an area external to the cylinder. As usedherein, the term “passageway” can be defined by any structure or voidcapable of communicating gas flow. It may include, for example, achannel or conduit completely or partially contained within at leastpart of the piston rod portion.

For example, in some exemplary embodiments of an engine according to thedisclosure, the passageway in the piston rod may render piston rod 40,including piston rod portions 42 and 43, at least partially hollow. Insome embodiments, the passageway may extend completely through piston50. An opening may be formed in one or each piston rod portion that maybe in fluid communication with the passageway of the piston rod, tothereby permit fluid to enter or exit the passageway through theopening. It is understood that a “fluid” may include gas, such as air.As shown in FIG. 2, first piston rod portion 42 may include opening 45.Opening 45 may be arranged at the end of first piston rod portion 42opposite piston 50, which may be an open end. Piston rod portion 43 mayalso include an opening 47 (see FIG. 3). In some embodiments, opening 47may be occluded. For example, piston rod portion 43 may include a plug49 that may be screwed into an open end of piston rod portion 43opposite piston 50.

FIG. 4A shows a cross-sectional view of piston kit 56. Piston kit 56 mayinclude one piston, such as piston 50, and a piston rod 40 that mayinclude two piston rod portions, such as first piston rod portion 42 andsecond piston rod portion 43. Piston kit 56 may include passageway 46extending through piston 50 into both combustion chambers 71 and 73.That is, piston kit 56 may include a passageway that extends throughpiston 50 and further extends beyond a first face of piston 50 andextends beyond a second face of piston 50 opposite to the first face.Furthermore, piston kit 56 may include plug 49. Plug 49 may beconfigured to occlude one end of piston rod 40. For example, FIG. 4Ashows plug 49 screwed into threads in second piston rod portion 43 toocclude opening 47. Plug 49 may seal opening 47 in an air-tight manner.Therefore, air introduced into piston rod 40 through opening 45 may beforced to exit piston rod 40 through either first opening 44 or secondopening 48. First opening 44, second opening 48, and opening 45 may bein fluid communication through passageway 46.

FIG. 4B shows another view of piston kit 56. Components of piston kit 56may be fastened to one another in a fixed manner. Piston 50 and pistonrod 40 may be formed separately from one another and may be fastened bya fastener. For example, screws 59 may be provided that fasten firstpiston rod portion 42, piston 50, and second piston rod portion 43 toone another. Furthermore, in some embodiments, first opening 44 andsecond opening 48 may each include a set of holes aligned at an axialposition of piston rod 40. For example, as shown in FIG. 4B, secondopening 48 b on second piston rod 43 may include a row of holes alignedwith plane XY that is perpendicular to axis A. The holes may extendcompletely through the wall of second piston rod 43 so that gases may becommunicated between passageway 46 and areas external to piston rod 40.

FIG. 4C is a cross-sectional view of second piston rod portion 43 takenat plane XY. In accordance with some embodiments, the holes may form anangle with a radial direction of piston rod 40. For example, the axis ofa hole of second opening 48 b may form an angle θ with the radialdirection of piston rod 40. Sidewalls of holes may extend in a directionparallel to an axis, the axis being at an angle to the radial directionof piston rod 40. Axes of other holes among the holes of second opening48 b may form the same or different angles with the radial direction ofpiston rod 40. In some embodiments, angle θ may be less than or equal to45 degrees. In some embodiments, angle θ may be in a range of 5 to 25degrees. Openings having angled sidewalls may be useful for imparting orencouraging swirl on gas flows travelling through piston rod 40 andthrough second opening 48 b. In some embodiments, there may be swirlvanes incorporated within piston rod 40. In addition to a circular hole,various other shapes may be employed for second opening 48 b.

By way of example with reference to FIG. 3, each piston rod portion 42and 43 may include a space 53, 55, respectively (e.g., hollowed outinternal portions of piston rod portions 42 and 43), forming at least apart of a conduit configured to communicate gas flow between an interiorof cylinder 12 and an area external to cylinder 12, such as areas 65 or67. Piston 50 may also include a space 54 that forms a part of theconduit configured to communicate gas flow between the interior ofcylinder 12 and external areas. Hollowed out regions may, for example,be a bore through a core of a piston rod portion or a piston. Spaces 53,54, and 55 may be contiguous. Passageway 46 may include spaces 53, 54,and 55.

As illustrated in FIG. 5, first combustion chamber 71 may be defined bya region between a side of piston 50 facing first head 14, and firsthead 14 of cylinder 12. Meanwhile, second combustion chamber 73 may bedefined by a region between an opposite side of piston 50 that facessecond head 15, and second head 15 of cylinder 12. Likewise, asillustrated in FIG. 10, second combustion chamber 73 at that time may bedefined by a region between a side of piston 50 facing second head 15,and second head 15 of cylinder 12. Meanwhile, first combustion chamber71 may be defined by a region between the side of piston 50 facing firsthead 14, and first head 14 of cylinder 12. For example, at a top deadcenter position at a respective end of cylinder 12, the combustionchamber at that time may be defined as the clearance volume. Similarly,the combustion chamber on the opposite side of the cylinder may bedefined as the remaining open volume in cylinder 12. Of course, it is tobe understood that each combustion chamber is a variable region thatincludes a swept volume on each side of the piston, and which iscompressed as the piston moves from one end of the cylinder to theopposite end of the cylinder. A swept volume may be defined as thevolume displaced by piston 50 during at least a part of itsreciprocating motion in cylinder 12. Total volume of a cylinder mayequal swept volume plus clearance volume.

Piston rod 40 may include at least one first opening, such as firstopening 44 in a first side of piston rod 40, and at least one secondopening, such as second opening 48 in a second side of piston rod 40,the second side being opposite the first side. In one exemplaryembodiment, as shown in FIG. 5, for example, first opening 44 mayinclude one or more ports in piston rod 40. First opening 44 may beconfigured to serve as an inlet for conveying gas into cylinder 12 viapassageway 46. While an exemplary embodiment shown in FIG. 5 shows firstopening 44 including a plurality of circular holes, a variety of shapesand arrangements may be used. For example, first opening 44 may includeelongated slots, grooves, openings having angled sidewalls, and thelike. As discussed above, FIG. 4C, which is a cross-sectional view ofthe exemplary second piston rod portion 43 shown in FIG. 4B, showssecond opening 48 b including a plurality of holes having angledsidewalls. In the case of angled sidewalls, an axis of openings may beangled with respect to a radial direction of piston rod 40. For example,as shown in FIG. 4C, an axis of a hole of second opening 48 b may forman angle greater than 0 relative to a radially normal direction ofsecond piston rod portion 43. Openings including angled sidewalls may beuseful to impart swirl onto fluid flows entering cylinder 12 and mayaffect flow characteristics. First opening 44 and second opening 48 maybe similarly formed.

A wall thickness of piston rod 40 may be varied along axis A. Forexample, as shown in FIG. 5, piston rod 40 may have thicker sidewalls ina region of first opening 44 or second opening 48. Sidewalls that arethicker in a region of the openings as compared to other parts of pistonrod 40 may be advantageous for alleviating stress concentrators at ornear the openings. Furthermore, thicker sidewalls may improve fatiguestrength of piston rod 40 without substantially increasing weight.

Piston rod 40, together with piston 50, may be configured to move in alinear reciprocating motion in cylinder 12. Piston 50 may be configuredto slide within cylinder 12 past a plurality of positions. Due to backand forth motion of piston rod 40, first opening 44 and second opening48 may selectively communicate fluid flow from outside cylinder 12 toinside cylinder 12. First opening 44 may be arranged on piston rod 40such that first opening 44 is configured to move into and out of firstcombustion chamber 71 to selectively communicate gas to first combustionchamber 71. Similarly, second opening 48 may be arranged on piston rod40 such that second opening 48 is configured to move into and out ofsecond combustion chamber 73 to selectively communicate gas to secondcombustion chamber 73.

In accordance with some embodiments of the disclosure, sliding action ofthe piston may enable gases to be introduced into cylinder 12, whilegases on opposite sides of piston 50 may be prevented from beingexchanged with one another. For example, a piston ring circumscribingpiston 50 may prevent leakage of compressed gases past piston 50.

In some embodiments, the cylinder head on each side of the engine blockmay include (e.g., be connected to or integrally formed with) an intakemanifold (not shown). In some embodiments, only one cylinder head mayinclude an intake manifold. Passageway 46 may be configured tocommunicate gas flow between first combustion chamber 71 and the intakemanifold at the first end of cylinder 12 when piston 50 is in a firstposition. Furthermore, passageway 46 may be configured to communicategas flow between second combustion chamber 73 and the intake manifoldwhen piston 50 is in a second position. Thus, for example, withreference to FIG. 5, gases from area 65 may enter cylinder 12 as secondopening 48 bridges cylinder head 14. With reference to FIG. 10, gas fromarea 65 may enter cylinder 12 as first opening 44 bridges cylinder head14.

A cylinder in accordance with embodiments of the disclosure may beclosed at both ends. For example, cylinder 12 of engine 10 may be closedat both ends thereof by cylinder heads 14 and 15, which may be connectedto the cylinder 12 by a plurality of fasteners. As used herein, the term“closed” does not require complete closure. For example, despite thatthe cylinder heads may have openings therein through which piston rod 40passes, the cylinder heads are still considered “closed” within themeaning of this disclosure.

In some embodiments, a peripheral portion of cylinder 12 may be providedwith cooling fins (not shown). Alternative configurations of the engine10 may include other external or internal features that assist with thecooling of the cylinder, such as water passageways formed internallywithin the cylinder walls or jacketing at least portions of the cylinderwalls for water cooling, and other configurations of cooling fins orother conductive or convective heat transfer enhancement featurespositioned along the exterior of a cylinder peripheral wall tofacilitate fluid cooling of the cylinder. Engine block 8 may includefluid passage 21 that may be used for circulating cooling water to aperipheral sidewall of cylinder 12. Fluid passage 21 may communicatewith fluid port 5 (see FIG. 1). Engine block 8 may further include fluidpassage 22 that may be used for circulating cooling water to cylinderheads 14 and 15. Fluid passage 22 may communicate with fluid port 6. Atemperature of cooling water in fluid passage 22 may be greater thanthat of fluid passage 21.

In accordance with exemplary embodiments of the disclosure, peripheralwall 13 of cylinder 12 may include at least one exhaust port betweenends of cylinder 12. By way of example only, cylinder 12 may include anexhaust port 18 in a peripheral side wall of cylinder 12 between firstcylinder head 14 and second cylinder head 15, the first and secondcylinder heads 14, 15 being positioned at ends of the cylinder. In theexemplary embodiment illustrated in FIGS. 5-14, a plurality ofdistributed exhaust ports 18 may be spaced about the circumference ofcylinder 12 at or approximately near a midpoint of cylinder 12 betweenthe opposite ends of the cylinder. Exhaust ports 18 may be of anysuitable size, shape, and distribution so as to accomplish the functionof exhausting gases from the cylinder. One or more of the exhaust portsmay, for example, be located in an axial central region of the cylinderperipheral wall, as illustrated in the figures. Although an exemplaryembodiment shown in the figures is configured symmetrically, withexhaust ports 18 located midway between the opposite ends of cylinder12, alternative embodiments may position the exhaust ports at one ormore radial planes intersecting the cylinder peripheral wall atlocations other than the exact midway point between cylinder heads 14and 15.

In accordance with some exemplary embodiments of the disclosure, one ormore exhaust ports 18 may be configured to communicate gas flow betweenthe first combustion chamber and outside the cylinder when piston 50 ison the second combustion chamber side of the one or more exhaust ports18, and may be configured to communicate gas flow between the secondcombustion chamber and outside the cylinder when the piston is on thefirst combustion chamber side of the one or more exhaust ports 18. Byway of example only, this can occur when, as illustrated in FIG. 8,piston 50 is located to the left of one or more exhaust ports 18,enabling conveyance of gas flow through the one or more exhaust ports 18from the combustion chamber to the right of piston 50. The one or moreexhaust ports 18 enable gas flow to a location “outside” the combustionchamber. That outside location may be on the side of the cylinder asillustrated, or conduits 19 associated with the engine might deliver thegases to other locations. In some embodiments, conduits 19 may beconnected to an exhaust manifold (not shown).

With reference to FIG. 5, an inlet manifold, which may includevestibules for communicating gases, such as air, may be connected to orformed integrally with each of cylinder heads 14, 15 at opposite ends ofcylinder 12. For example, first vestibule 30 may be formed at a firstend on a side of cylinder 12, and second vestibule 31 may be formed at asecond end on the opposite side of cylinder 12. Each of vestibules 30and 31 may include a piston rod opening, such as opening 28, which isaxially aligned with axis A, and side opening 33, or other openings.Side opening 33 may be positioned at a distal end of the inlet manifold,as shown, or at any location along the outer periphery of the inletmanifold. As shown in FIG. 5, side opening 33 may be sealed.Furthermore, first vestibule 30 and second vestibule 31 may each includea bushing 41. Bushings 41 may be provided for aligning, supporting,guiding, and sealing (by, e.g., means of a dedicated seal) an end offirst and second piston rod portions 42, 43 while allowing first andsecond piston rod portions 42, 43 to slide in and out of a respectiveopening 28. In some embodiments, side opening 33 may be opened to allowinlet air to enter.

In some embodiments, an inlet chamber 32 may be provided for allowinginlet air to enter engine 10. For example, as illustrated in FIG. 5,inlet chamber 32 may be arranged adjacent to first vestibule 30.Passageway 46 may be configured to deliver gas from inlet chamber 32 tocylinder 12. Gas may be delivered from inlet chamber 32 to secondcombustion chamber 73 in the first position of piston 50, as shown inFIG. 5, and gas may be delivered from inlet chamber 32 to firstcombustion chamber 71 in the second position of piston 50, as shown inFIG. 10. Inlet chamber 32 may include inlet opening 29. Inlet opening 29may be configured to direct inlet gases, such as air, into the inletmanifold in a direction along axis A. Inlet opening 29 may be configuredto direct gases into passageway 46 substantially through opening 45 infirst piston rod portion 42. Although the inlet manifold of theexemplary embodiment shown in FIG. 5 is illustrated as having asubstantially cylindrically-shaped configuration, alternativeembodiments may provide one or more inlet manifolds with other shapedprofiles or cross sections, or may incorporate the inlet manifolds atleast partially within cylinder heads 14, 15 as one or more internalpassageways defined within each of the cylinder heads at each end ofcylinder 12. Inlet opening 29 may include a substantially cylindricalmember connected to inlet chamber 32 along axis A, among otherconfigurations.

Supplying air from one end of engine 10 through inlet chamber 32 mayprovide a number of benefits. For example, air may be directed to flowinto engine 10 substantially in a direction parallel to axis A, whichmay be in a longitudinal direction of engine 10. Piston rod 40 mayinclude opening 45 and passageway 46, which is arranged to extendsubstantially along axis A, and thus, air may flow through piston rod 40with less turbulence, which may reduce pressure losses. Furthermore,regions of stagnation may be minimized. As compared with providing airentering through side opening 33, for example, providing inlet chamber32 may result in improved flow characteristics.

Air may be introduced into engine 10 through a vestibule among firstvestibule 30 and second vestibule 31. Air may be configured to flow fromarea 65 or area 67 (external to cylinder 12) to an interior of cylinder12, including first combustion chamber 71 or second combustion chamber73. Air may be introduced into engine 10 through inlet chamber 32 via avestibule among first vestibule 30 and second vestibule 31. For example,when piston 50 is in the first position, air may travel through inletopening 29, and then air may be in communication with area 65,passageway 46, and second combustion chamber 73, as shown in FIG. 5.Also, when piston 50 is in the second position, air may travel throughinlet opening 29, and then air may be in communication with area 65,first combustion chamber 71, passageway 46, and area 67.

Engine 10 may include a first isolation area on one side of cylinder 12and a second isolation area on an opposite side of cylinder 12. Thefirst isolation area may include area 65, and the second isolation areamay include area 67. The first and second isolation areas may beconfigured to isolate non-active piston rod parts during alternatecylinder charges. For example, when piston 50 is in the first position,air may travel from inlet opening 29, through passageway 46, and intosecond combustion chamber 73, as shown in FIG. 5. In the position asshown in FIG. 5, air from inlet 29 may not be in communication with area67. Thus, area 67 may isolate a portion of piston rod 40. A non-activepart of piston rod 40 may refer to a portion through which gases do nottravel to reach a combustion chamber.

Air may be supplied to engine 10 through a single air supply. The airsupply may be flow-connected to passageway 46 in piston rod 40 such thatgas flow is communicated between first combustion chamber 71 and the airsupply when piston 50 is in the first position. Furthermore, passageway46 may be configured to communicate gas flow between second combustionchamber 73 and the air supply when piston 50 is in a second position. Itis understood that air may be introduced into engine 10 by openingsother than inlet opening 29. For example, air may be introduced via oneor more of side openings 33. Air may be introduced through side opening33 in first vestibule 30 while other openings (such as inlet opening 29)are sealed off. Thus, gas may be delivered from first vestibule 30 tocylinder 12. Alternatively, air may be introduced through side opening33 in second vestibule 31 while other openings are sealed off. Sideopening 33 may be configured such that air is directed to flow intoengine 10 substantially in a direction perpendicular to axis A. Sideopening 33 may be configured to direct gases into passageway 46substantially through first opening 44, or through second opening 48.Configuring openings to introduce air into engine 10 by way of, e.g.,inlet opening 29, or side opening 33, may allow design flexibility inconsideration of packaging constraints. For example, in someembodiments, when air is introduced through inlet opening 29, engine 10may be packaged into a long, thin space. In other embodiments, when airis introduced through side opening 33, engine 10 may be packaged into ashort, compact space.

In some embodiments, both first vestibule 30 and second vestibule 31 maybe configured to supply air to engine 10. For example, both side opening33, provided on first vestibule 30, and side opening 33, provided onsecond vestibule 31, may be opened. The single air supply may supply airto both first vestibule 30 and second vestibule 31.

Each of the cylinder heads 14, 15 may further include an injector 34(see FIG. 1) that opens into an annular or toroidal-shaped recess 36formed in or contiguous with a flame face of a fire deck of eachcylinder head at each end of the cylinder 12 in facing relationship withthe combustion chambers at each end of cylinder 12 (see FIG. 3). Recess36 may be toroidal and may impart swirl flow to fuel gas injected byinjectors 34 to facilitate more complete combustion of the gases withinthe combustion chambers. Each of cylinder heads 14, 15 may also includea cavity for accommodating and mounting a spark plugs 38. Each ofcylinder heads 14, 15 may also include a cavity for accommodating andmounting bushings 41 for aligning, supporting, guiding, and sealing (by,e.g., means of a dedicated seal) a respective one of piston rod portions42, 43 that is supported by, and passes through each of the cylinderheads 14, 15 at opposite ends of the cylinder 12. This is one example ofhow piston rod portions may extend from faces of a double-faced pistonthrough a combustion chamber. Regardless of the particular details ofany aperture through which the piston rods may extend at ends of thecylinder, a piston rod that extends to at least an end of the cylinderis said to extend through a combustion chamber within the meaning ofthis disclosure.

A double-faced piston consistent with embodiments of the presentdisclosure may be configured to travel in a first stroke from a firstend of the cylinder to an opposite second end of the cylinder, and in asecond stroke from the second end of the cylinder back to the first end.This length of travel is illustrated, by way of example, in FIGS. 5-14,where FIG. 5 represents the beginning of a first stroke, FIG. 10represents the end of the first stroke, which may also be the beginningof a second stroke, and FIGS. 6-9 represent exemplary intermediatepositions. FIG. 10 may represent the beginning of the second stroke,FIG. 14 may represent the end of the second stroke, and FIGS. 10-12 mayrepresent some exemplary intermediate positions.

Piston 50 may be slidable between a plurality of positions throughoutcylinder 12. For example, piston 50 may be slidable between a firstposition and a second position. The first position may be a positionwhere first opening 44 is outside cylinder 12 and second opening 48 isinside cylinder 12. At the first position, second opening 48 may beinside the second combustion chamber of cylinder 12. The second positionmay be a position where first opening 44 is inside cylinder 12 andsecond opening 48 is outside cylinder 12. At the second position, firstopening 44 may be inside the first combustion chamber of cylinder 12.The first position may correspond to the beginning of a first stroke ofengine, and the second position may correspond to the end of the firststroke.

According to various exemplary embodiments of the present disclosure,the piston may be sized relative to the cylinder to enable an expansionstroke portion of each stroke wherein the piston travels under gasexpansion pressure, and a momentum stroke portion of each stroke for theremainder of the stroke following the expansion stroke portion. Theexpansion stroke portion of each of the first and second strokes of thepiston is the portion of travel when the piston directly moves under theexpansion pressure of combustion. For example, the expansion portion ofa stroke may be defined as the portion from a combustion position of thepiston at each end of the cylinder to the point at which exhaust gasesmay be exchanged between the combustion chamber in which ignition ofcombustion gases (including air and fuel) has just occurred and an areaexternal to the cylinder. In some embodiments, the termination of theexpansion stroke portion may coincide with a position where the pistonbegins to expose an exhaust port.

At the combustion position of the piston during each stroke, a clearancevolume may remain between each of the opposite faces of the piston and arespective end of the cylinder as closed off by the cylinder heads 14,15. The combustion gases that are introduced into the combustion chamberbefore the piston reaches the combustion position may be compressed intothe remaining clearance volume on that side of the piston between thepiston face and the fire deck of the cylinder head. The compressedgasses in the clearance volume may be compressed into such a smallvolume that gas pressure prevents piston 50 from contacting a respectiveone of cylinder heads 14, 15. The compressed gases, which in someembodiments may include a fuel/air mixture, may be ignited by either aspark, or by self-ignition resulting at least in part from thecompression of the combustion gases.

The combustion position may be a point along axis A corresponding to thebeginning of a combustion event in cylinder 12. The combustion positionmay be a point where a predetermined compression ratio of gases in acombustion chamber is reached. For example, the combustion position maybe a point where a compression ratio of a combustion chamber reaches10:1. Combustion may be initiated at the combustion position byactivating spark plug 38. The combustion position may be a point wherepiston 50 changes direction. The combustion position may be a zero-speedposition of piston 50. In some embodiments, engine 10 may be configuredso that piston 50 decelerates to zero-speed at the moment thatcombustion is initiated. The combustion position may correspond to thefirst position mentioned above, which may correspond to the beginning ofthe first stroke of engine 10. In some embodiments, the combustionposition may be a fixed position. However, it will be understood thatthe combustion position may be a variable position that may bedetermined, for example, by when spark plug 38 is activated, or whenauto-ignition is configured to occur.

The expansion stroke portion of each stroke occurs after the ignition ofthe compressed combustion gases as chemical energy from the combustionin each combustion chamber is converted into kinetic energy (e.g.,mechanical work) of the piston. Simultaneously with the expansion strokeportion of each stroke on one side of the piston, gas flow may occur forat least a portion of the expansion stroke portion between thecombustion chamber on the opposite side of the piston and the intakemanifold at the opposite end of the cylinder, as well as through exhaustports.

In some embodiments, useful work may be extracted from engine 10 by, forexample, mechanically coupling one end of piston rod 40 to an output.Second piston rod portion 43 may be connected to an apparatus at an endopposite piston 50 that may be configured to convert reciprocatinglinear motion to useful work. For example, a linear actuator may becoupled to second piston rod portion 43 at opening 47 (see, e.g., FIG.5). Plug 49 may be integral with an actuator configured to convertlinear motion to work. Such an actuator may include a generator, forexample.

Referring back to FIG. 5, at the beginning of an expansion strokeportion of a stroke where piston 50 moves from the right end of cylinder12 to the left end, piston 50 may be in a first position. From thisfirst position, gas flow may occur between the combustion chamber on theleft side of piston 50 and inlet chamber 32, which may be on the rightside of cylinder 12. Also from this first position, gas flow may alsooccur between the combustion chamber on the left side of piston 50 andconduits 19 leading to an outside of cylinder 12 through one or moreexhaust ports 18. The communication of gases between the combustionchamber on the left side of piston 50 and conduits 19 may continue untilthe left face of piston 50 has moved past the one or more exhaust ports18, acting as an exhaust valve and shutting off communication betweenthe left combustion chamber and the one or more exhaust ports 18.Additionally, before piston 50 has closed off the one or more exhaustports 18, second opening 48 closest to the left face of the piston mayhave moved outside of the left combustion chamber, thereby closing offcommunication of gases between inlet chamber 32 and the left combustionchamber through passageway 46 of piston rod 40. Thus, piston rod 40 maybe configured such that a gas intake phase in a combustion chamber ofcylinder 12 ends before an exhaust phase. A length from a proximal faceof piston 50 to a proximal end of second opening 48 may be set such thatfluid communication between second opening 48 and interior of cylinder12 is stopped before fluid communication between exhaust ports 18 andinterior of cylinder 12. For example, a length from the left face ofpiston 50 to the right end of second opening 48 may be set to be greaterthan a length of piston travel in the expansion phase. The length fromthe left face of piston 50 to the right end of second opening 48 may begreater than the length of piston travel in the expansion phase by atleast a quarter of the length of piston 50. Lengths may be set tocontrol, for example, a pressure buildup in passageway 46, as will bediscussed later.

As shown in FIG. 6, piston 50 may move to a further position. At theposition shown in FIG. 6, second opening 48 is no longer inside cylinder12, and thus, fluid communication between passageway 46 of piston rod 40and the interior of cylinder 12 via second opening 48 is stopped.

According to some embodiments, a length (in axial direction A) of piston50, a length of cylinder 12, a location of exhaust ports 18, and alocation of first and second openings 44, 48 in first and second pistonrod portions 42, 43 may be arranged such that when piston 50 is in acombustion phase in the first combustion chamber, piston 50 blocksexhaust ports 18 from communicating with the first combustion chamberand first opening 44 in first piston rod portion 42 is outside of thefirst combustion chamber, while simultaneously exhaust ports 18 are influid communication with the second combustion chamber, and secondopening 48 in second piston rod portion 43 is within the secondcombustion chamber. This may be accomplished by various alternativestructures. By way of example only with reference to the figures, thelength of piston 50, the length of cylinder 12, the location of exhaustports 18, and the location of openings 44 and 48 in each of first andsecond piston rod portions 42, 43 extending from opposite faces ofpiston 50 may be arranged such that when piston 50 is in a combustionphase in a first combustion chamber on one side of piston 50, piston 50blocks exhaust ports 18 from communicating with the first combustionchamber. First opening 44 to the one side of piston 50 remains outsideof the first combustion chamber, thereby preventing communication ofgases between inlet chamber 32 on that one side of piston 50 and thefirst combustion chamber.

Simultaneously, exhaust ports 18 are in fluid communication with thesecond combustion chamber on the opposite side of piston 50, and secondopening 48 in second piston rod portion 43 may be located within thesecond combustion chamber. Similarly, when piston 50 is in anothercombustion stage in the second combustion chamber on the opposite side,piston 50 blocks exhaust ports 18 from communicating with the secondcombustion chamber. Second opening 48 to the second side of piston 50remains outside of the second combustion chamber, thereby preventingcommunication of gases between inlet chamber 32 on the second side ofpiston 50 and the second combustion chamber. Simultaneously, exhaustports 18 are in fluid communication with the first combustion chamber onthe first side of piston 50, and first opening 44 in first piston rodportion 42 may be located within the first combustion chamber.

According to some embodiments, the length of piston 50, a length ofcylinder 12, a location of exhaust ports 18, and a location of first andsecond openings 44, 48 in first and second piston rod portions 42, 43may be arranged such that when piston 50 continues to move through thefirst stroke, the combustion phase ends (concurrent with exhaust phasebeginning) before first opening 44 enters cylinder 12. FIG. 7illustrates a position where combustion on the right side of piston 50may end while an exhaust phase may begin. The precise location wherecombustion ends and exhaust begins on right side of piston 50 maycorrespond to a position where the right face of piston 50 reaches theright edge of exhaust ports 18. At this position, first opening 44 isoutside cylinder 12.

Following an expansion stroke portion (also called a combustion phase),piston 50 may continue to move in a momentum stroke portion for aremainder of the stroke. The momentum stroke portion of each strokeencompasses the remaining portion of the stroke following the expansionstroke portion. In accordance with embodiments of the disclosure,substantially the entire momentum stroke portion of the second stroke onthe second combustion chamber side of piston 50 may coincide withcompression of gases in the first combustion chamber. That is, themomentum that follows an expansion portion of the stroke in onecombustion chamber may be used to compress gasses in the othercombustion chamber. This may be made possible by an engine structurewhere an end of an expansion in one combustion chamber may correspondwith a position different from the combustion position in an opposingcombustion chamber. Such an engine design may enable further pistontravel following an expansion portion of the stroke. In someembodiments, the further piston travel during the momentum portion ofthe stroke may be at least a width of the piston. A “width” of thepiston may be synonymous with a length of the piston in the direction ofaxis A. In some embodiments the further piston travel may be multipletimes a width of the piston. In other embodiments, the further pistontravel may be a fraction of the width of the piston, for example atleast a half a width of the piston. In yet other embodiments, thefurther travel may be at least a quarter a width of the piston. Furthertravel of piston 50 beyond at least one of exhaust ports 18 may bereferred to as piston overshoot.

During the momentum stroke portion of each stroke, gases may beexchanged between the combustion chamber where ignition of combustiongases has just occurred and an area external to cylinder 12. Theexchange of gases may occur through exhaust ports formed in peripheralwall 13 of cylinder 12. The exchange of gases may be aided byintroduction of air into cylinder 12 through a passageway in the pistonrod portion connected to the piston and extending from a location withinthe at least one combustion chamber to an area external to the cylinder.By way of one example with reference to FIGS. 5-10, the positions ofpiston 50 and piston rod portions 42, 43 are shown during a first strokefrom the far-right position of piston 50 in cylinder 12, as in FIG. 5,to the far-left position of piston 50 in cylinder 12, as in FIG. 10.FIGS. 10-14 show the positions of piston 50 and piston rod portions 42,43 during a second stroke from the far-left position of piston 50 incylinder 12, as in FIG. 10, to the far-right position of piston 50 incylinder 12, as in FIG. 14. The far-left and far-right positions ofpiston 50 in cylinder 12 may be referred to as the combustion positionfor the stroke in which the combustion gases have been compressed andignition of the gases at the beginning of a combustion phase isoccurring. When piston 50 is in the far-right position, as in FIG. 5,and ignition is occurring for the combustion gases that have beencompressed into a clearance volume between the right face of piston 50and cylinder head 14 at the right end of cylinder 12, piston 50 is atthe combustion position for the stroke from the right end to the leftend of cylinder 12 as viewed in FIGS. 5-10. Similarly, when piston 50 isin the far left position of FIG. 10 and ignition is occurring for thecombustion gases that have been compressed into a clearance volumebetween the left face of piston 50 and cylinder head 15 at the left endof cylinder 12, piston 50 is at the combustion position for the strokefrom the left end to the right end of cylinder 12 as viewed in FIGS.10-14.

FIG. 5 illustrates a position where piston kit 56 is at a starting pointof a first stroke that may be defined as a stroke from the right end ofcylinder 12 to the left end of cylinder 12. Components of piston kit 56,including first piston rod portion 42, piston 50, and second piston rodportion 43 may be joined together such that piston kit 56 travels as aunit. In the position shown in FIG. 5, a combustion phase may begin infirst combustion chamber 71 on the right side of piston 50. Meanwhile,on the opposite side of piston 50, gas may be introduced into cylinder12 through a flow path including passageway 46 in piston rod 40. Forexample, gas may be introduced into inlet chamber 32 via inlet opening29. The gas may be air. The gas may be pressurized relative to ambientatmospheric pressure. First piston rod portion 42 includes opening 45,and thus, the gas from inlet chamber 32 is in fluid communication withpassageway 46 of piston rod 40. Furthermore, because opening 47 insecond piston rod portion 43 may be occluded by plug 49 (or by virtue ofsecond vestibule 31 being sealed off in an air-tight manner, forexample), gas is forced into cylinder 12 via second opening 48. In thisposition, cylinder 12 on the left side of piston 50 may begin to fillwith gas. Because exhaust ports 18 are open, some gas may escape.

As combustion begins, piston 50 will move to the left. As shown in FIG.6, piston 50 continues to move from the combustion position for thestroke from the right end of cylinder 12 to the left end of cylinder 12.FIG. 6 illustrates a position where second opening 48 in second pistonrod portion 43 reaches cylinder head 15. Accordingly, introduction ofgas into cylinder 12 stops.

FIG. 7 illustrates a position where the combustion phase in firstcombustion chamber 71 on the right side of piston 50 may end and where acompression phase in second combustion chamber 73 on the left side ofpiston 50 may begin. The combustion phase may end when piston 50 beginsto expose exhaust ports 18 on the right side of piston 50. At the sametime, an exhaust phase on the right side of piston 50 may begin. Thus,the exhaust phase may begin when first combustion chamber 71 becomesopen. The compression phase may begin when piston 50 completely coversexhaust ports 18 on the left side of piston 50. Thus, the compressionphase may begin when second combustion chamber 73 becomes sealed. Awidth of piston 50 may be equal to that of exhaust ports 18. Although insome embodiments combustion on the right side of piston 50 may endsubstantially simultaneously with compression beginning on the left sideof piston 50, the present disclosure is not so limited. Some embodimentsmay allow combustion and compression phases on opposite sides of piston50 to begin at different times. For example, a width of piston 50 may begreater than a width of exhaust ports 18, and thus, compression maybegin while the combustion phase on the opposite side of piston 50 isstill occurring. Similarly, a width of piston 50 may be less than awidth of exhaust ports 18, and thus, the combustion phase may end beforethe compression phase begins on the opposite side of piston 50.

As piston 50 continues to move to the left, piston 50 may reach aposition where piston 50 has just passed the centrally located exhaustports 18, as shown in FIG. 8. At this point, exhaust ports 18 are fullyexposed on the right side of piston 50. Thus, first combustion chamber71 on the right side of piston 50 is in fluid communication with exhaustports 18 and exhaust gases from the combustion exit the combustionchamber. Therefore, the expansion stroke portion of the stroke hasended, and the piston is continuing to travel toward the left end ofcylinder 12 in the momentum stroke portion as a result of inertiaremaining after the end of the expansion stroke portion.

As shown in FIGS. 8 and 9, piston 50, first piston rod portion 42 on theright side of piston 50, and exhaust ports 18 may be configured suchthat piston 50 passes all of exhaust ports 18 as the piston moves fromthe right end of cylinder 12 toward the left end of cylinder 12 beforefirst opening 44 in first piston rod portion 42 enters first combustionchamber 71 on the right side of piston 50. As shown in FIG. 9, piston 50has moved completely to the left of exhaust ports 18 by the time firstopening 44 in the right piston rod portion 42 begins to enter firstcombustion chamber 71 on the right side of piston 50 to permit gas flowbetween first combustion chamber 71 and first opening 44. This relativesizing and spacing of the various components may allow exhaust gasesgenerated in first combustion chamber 71 to begin exiting from theexhaust ports 18 before fresh pre-compressed air or other gases areintroduced into first combustion chamber 71 through first piston rodportion 42 on the right side of piston 50. In various alternativeembodiments, the precise placement of openings through piston rodportions 42, 43 relative to the opposite faces of piston 50 may bevaried such that the closest inlet port to each face of the pistonenters the respective combustion chamber on the same side of the pistonshortly after the face of the piston has passed the near edge of theexhaust ports, thereby allowing exhaust gases to begin exiting therespective combustion chamber a short time before introduction of thefresh pre-compressed air or other gases (see, e.g., FIGS. 9 and 14).

Shortly after piston 50 has passed exhaust ports 18 during the momentumstroke portion of the stroke from the right end of cylinder 12 to theleft end of cylinder 12, as shown in FIG. 9, the edges of first opening44 in first piston rod portion 42 closest to the right face of piston 50start to enter first combustion chamber 71 on the right side of piston50. At this point, a scavenging phase may occur on the right side ofpiston 50 as a result of gases, such as fresh air, being introduced intofirst combustion chamber 71 through first opening 44 of first piston rodportion 42. Scavenging may refer to the process of pushing exhausted gasincluding combustion products out of cylinder 12 and drawing in freshair for the next cycle. A certain amount of scavenging may be desired sothat the next cycle does not begin with a mix of exhaust gases ratherthan substantially clean air. First opening 44 may be configured suchthat when piston 50 is in the momentum stroke portion of the firststroke from the right end to the left end of cylinder 12, gas flow maybe continuously communicated between first combustion chamber 71 and anarea external to cylinder 12. In the exemplary embodiment shown in FIG.10, fresh, pre-compressed air may be introduced into first combustionchamber 71 from inlet chamber 32 located opposite cylinder head 14 orintegral with cylinder head 14 on the right end of cylinder 12.Simultaneously, exhaust gases may be scavenged from first combustionchamber 71 by the incoming pre-compressed air or other gases and forcedout through exhaust ports 18.

Some aspects of the present disclosure may involve cylinder 12 andpiston 50 being sized such that the expansion stroke portion of thefirst stroke on a first side of piston 50 as piston 50 moves from thefirst end of cylinder 12 to the second end of cylinder 12 coincides withat least one of a scavenging phase and a gas boost phase on a secondside of piston 50. A similar coincidence may occur in connection withthe second stroke. By way of non-limiting example with reference to thefigures, as piston 50 continues to move toward the left end of thecylinder, as shown in FIGS. 9 and 10, gas flow may be continuouslycommunicated between first combustion chamber 71 and an area external tocylinder 12. The continuous flow of pre-compressed air or other gasesintroduced from inlet chamber 32 into first combustion chamber 71 mayassist with cooling of cylinder 12 as well as scavenging of exhaustgases from first combustion chamber 71 and boosting the gas pressure infirst combustion chamber 71. A similar coincidence is illustrated forthe second stroke in FIGS. 13 and 14. In some embodiments, thecoincidence of compression on one side of cylinder 12 with scavengingand gas boost on the other side of cylinder 12 may precisely correspond.In other embodiments compression on one side of cylinder 12 maysubstantially overlap with scavenging and gas boost on the other side ofcylinder 12.

Some aspects of the present disclosure may involve cylinder 12 andpiston 50 being sized such that the momentum stroke portion of the firststroke on a first side of piston 50 as piston 50 moves from the firstend of cylinder 12 to the second end of cylinder 12 coincides with acompression phase in the combustion chamber on a second side of piston50. By way of non-limiting example, simultaneously with the momentumstroke portion of the first stroke from the right end of cylinder 12 tothe left end of cylinder 12, after piston 50 has moved past exhaustports 18 toward the left end of cylinder 12, gases on the left side ofpiston 50 are compressed during a compression phase on the left side ofpiston 50. When piston 50 is all the way to the left, as shown in FIG.10, the combustion gases on the left side of piston 50 will have beencompressed into the remaining clearance volume of second combustionchamber 73 and ignition may occur to begin the second stroke.

As best seen by way of non-limiting example in FIGS. 5-14, cylinder 12and piston 50 may be sized such that a total distance piston 50 travelsduring the first stroke from the right end of cylinder 12 to the leftend of cylinder 12, or during the second stroke from the left end ofcylinder 12 to the right end of cylinder 12, may be substantiallygreater than a distance piston 50 travels during the expansion strokeportion of either stroke. In some exemplary embodiments, cylinder 12 andpiston 50 may be sized such that the total distance piston 50 travelsduring each stroke from one end of cylinder 12 to the opposite end ofcylinder 12 may exceed the distance piston 50 travels during theexpansion stroke portion of the stroke by at least the length of piston50 from one face to the opposite face. In other exemplary embodiments,cylinder 12 and piston 50 may be sized such that a total distance piston50 travels in each stroke exceeds, by at least the length of piston 50,a distance traveled by piston 50 during compression of gases on one sideof piston 50. The length of the piston 50 from one face to the oppositeface in the exemplary embodiment shown in the figures may be less than ½of a distance from at least one of cylinder heads 14, 15 to centrallylocated exhaust ports 18. This configuration and relative sizing of thepiston and cylinder may allow for a significantly greater length of thetotal stroke for the piston in each direction during which freshpre-compressed air or other gases may be introduced into the cylinderfor the purposes of scavenging exhaust gases and cooling the cylinderafter each combustion occurs at opposite ends of the cylinder.

At the beginning of an expansion stroke portion of a stroke from theleft end of cylinder 12 to the right end, as shown in FIG. 10, gas flowmay occur between first combustion chamber 71 on the right side ofpiston 50 and inlet chamber 32 on the right side of cylinder 12, andbetween first combustion chamber 71 on the right side of piston 50 andexhaust ports 18. The communication of gases between first combustionchamber 71 and exhaust ports 18 may continue until the right face ofpiston 50 has moved past exhaust ports 18, acting as an exhaust valveand shutting off communication between first combustion chamber 71 andexhaust ports 18. Additionally, before piston 50 has closed off exhaustports 18, first opening 44 of first piston rod portion 42 may have movedoutside of first combustion chamber 71, thereby closing offcommunication of gases between inlet chamber 32 and first combustionchamber 71 through piston rod 40.

The length of piston 50, the length of cylinder 12, the location ofexhaust ports 18, and the location of openings 44, 48 in each of thefirst and second piston rod portions 42, 43 extending from oppositefaces of piston 50 may be arranged such that when piston 50 is in acombustion phase in second combustion chamber 73 on the left side ofpiston 50, piston 50 blocks exhaust ports 18 from communicating withsecond combustion chamber 73. Meanwhile, second opening 48 to the leftside of piston 50 remains outside of second combustion chamber 73,thereby preventing communication of gases between inlet chamber 32 andsecond combustion chamber 73. Simultaneously, exhaust ports 18 are influid communication with first combustion chamber 71 on the right sideof piston 50, and first opening 44 in first piston rod portion 42 islocated within first combustion chamber 71.

The momentum stroke portion of each stroke may encompass the remainingportion of the stroke following the expansion stroke portion. During themomentum stroke portion of each stroke, gases may be exchanged betweenthe combustion chamber where ignition of combustion gases has justoccurred and an area external to the cylinder. The exchange of gases mayoccur through exhaust ports formed in the peripheral wall of thecylinder. FIGS. 10-14 show the positions of piston 50 and piston rodportions 42, 43 during a second stroke from the far-left position of thepiston in FIG. 10 to the far-right position of the piston in FIG. 14. Asdiscussed above, the far-left and far-right positions of piston 50 incylinder 12 may be referred to as combustion positions for therespective strokes, in which the combustion gases have been compressedand ignition of the gases at the beginning of a combustion phase may beoccurring. When piston 50 is in the far-left position as in FIG. 10 andignition is occurring for the combustion gases that have been compressedinto a clearance volume between the left face of piston 50 and cylinderhead 15 at the left end of cylinder 12, piston 50 is at the combustionposition for the stroke from the left end to the right end of cylinder12, as viewed in FIGS. 10-14.

As combustion begins in the second stroke, piston 50 will move to theright. As shown in FIG. 11, piston 50 continues to move from thecombustion position for the stroke from the left end of cylinder 12 tothe right end of cylinder 12. FIG. 11 illustrates a position where firstopening 44 in first piston rod portion 42 reaches cylinder head 14.Accordingly, introduction of gas into cylinder 12 stops.

FIG. 12 illustrates a position where the combustion phase in secondcombustion chamber 73 on the left side of piston 50 may end and where acompression phase in first combustion chamber 71 on the right side ofpiston 50 may begin. The combustion phase may end when piston 50 beginsto expose exhaust ports on the left side of piston 50. At the same time,an exhaust phase on the left side of piston 50 may begin. Thus, theexhaust phase may begin when second combustion chamber 73 becomes open.The compression phase may begin when piston 50 completely covers exhaustports 18 on the right side of piston 50. Thus, the compression phase maybegin when first combustion chamber 71 becomes sealed. According to aratio of width of piston 50 to that of exhaust ports 18, the timing ofthe end of the combustion phase on the left side of piston 50 andbeginning of compression on the right side of piston 50 may be adjusted.

As the piston continues to move to the right, piston 50 may reach aposition where piston 50 passes the centrally located exhaust ports 18,as shown in FIG. 13. At this point, exhaust ports 18 have been fullyexposed on the left side of piston 50. Thus, second combustion chamber73 on the left side of piston 50 is in fluid communication with exhaustports 18 and exhaust gases from the combustion that occurred on the leftside of piston 50 during the expansion stroke portion of the secondstroke may exit second combustion chamber 73. Therefore, the expansionstroke portion of the second stroke has ended, and the piston iscontinuing to travel toward the right end of cylinder 12 in the momentumstroke portion as a result of inertia remaining after the end of theexpansion stroke portion.

As shown in FIG. 13, the piston 50, second piston rod portion 43 on theleft side of piston 50, and exhaust ports 18 may be configured such thatpiston 50 passes all of exhaust ports 18 as the piston moves from theleft end of cylinder 12 toward the right end of cylinder 12 beforesecond opening 48 in second piston rod portion 43 enters secondcombustion 73 chamber on the left side of piston 50. As shown in FIG.13, piston 50 has moved completely to the right of exhaust ports 18 bythe time second opening 48 in the left piston rod portion 42 begins toenter second combustion chamber 73 on the left side of piston 50 topermit gas flow between second combustion chamber 73 and second opening48. This relative sizing and spacing of the various components may allowexhaust gases generated in second combustion chamber 73 to begin exitingfrom exhaust ports 18 before fresh pre-compressed air or other gases areintroduced into second combustion chamber 73 through second piston rodportion 43 on the left side of piston 50. In various alternativeembodiments, the precise placement of openings through piston rodportions 42, 43 relative to the opposite faces of piston 50 may bevaried such that the closest inlet port to each face of the pistonenters the respective combustion chamber on the same side of the pistonshortly after the face of the piston has passed the near edge of theexhaust ports, thereby allowing exhaust gases to begin exiting therespective combustion chamber a short time before introduction of thefresh pre-compressed air or other gases.

Shortly after piston 50 has passed exhaust ports 18 during the momentumstroke portion of the stroke from the left end of cylinder 12 to theright end of cylinder 12, as shown in FIG. 13, the edges of secondopening 48 in second piston rod portion 43 closest to the left face ofpiston 50 start to enter second combustion chamber 73. At this point, ascavenging phase may occur on the left side of piston 50 as a result ofgases such as fresh air being introduced into second combustion chamber73 through second opening 48 of second piston rod portion 43. Secondopening 48 may be configured such that when piston 50 is in the momentumstroke portion of the second stroke from the left end to the right endof cylinder 12, gas flow may be continuously communicated between secondcombustion chamber 73 and an area external to cylinder 12. In theexemplary embodiment shown in FIG. 14, fresh, pre-compressed air may beintroduced into second combustion chamber 73 from inlet chamber 32.Simultaneously, exhaust gases may be scavenged from second combustionchamber 73 by the incoming pre-compressed air or other gases and forcedout through exhaust ports 18.

As the piston continues to move toward the right end of the cylinder, asshown in FIGS. 13 and 14, gas flow may be continuously communicatedbetween second combustion chamber 73 and an area external to thecylinder. The continuous flow of pre-compressed air or other gasesintroduced from inlet chamber 32 into second combustion chamber 73 mayassist with cooling of cylinder 12 as well as scavenging of exhaustgases from second combustion chamber 73, and boosting the gas pressurein second combustion chamber 73. Simultaneously with the momentum strokeportion of the second stroke from the left end of the cylinder to theright end of the cylinder, after piston 50 has moved past the exhaustports 18 toward the right end of cylinder 12, gases on the right side ofpiston 50 are compressed during a compression phase on the right side ofpiston 50. When the piston is all the way to the right, as shown in FIG.14, the combustion gases on the right side of the piston will have beencompressed into the remaining clearance volume of first combustionchamber 71 and ignition will occur to begin another stroke from theright end of the cylinder to the left end of the cylinder. Thereafter,further strokes may continue in this manner.

In accordance with some embodiments of the present disclosure,regardless of other particular structures in the engine, a cylinder anda double-faced piston may be sized such that a total distance the pistontravels during a first stroke is substantially greater than a distancethe piston travels during an expansion stroke portion of the firststroke. By way of example with reference to FIGS. 5-10, the totaldistance of piston travel may be measured from the combustion positionon the right side of cylinder 12, as illustrated in FIG. 5, for example,to the combustion position on the left side of cylinder 12, asillustrated in FIG. 10, for example. This total distance traveled issubstantially greater than the expansion portion of the stroke whichoccurs when, in the progression of FIGS. 5-10, piston 50 reaches atleast one of exhaust ports 18. In some embodiments, the end of theexpansion stroke may be marked by other occurrences, such as the openingof a mechanical valve, or the cessation of expansion in some othermanner. Regardless of how the expansion stroke portion ends, suchembodiments are contemplated to be within the scope of this disclosureso long as the total distance of travel is substantially greater thanthe expansion portion alone. By way of non-limiting examples, the totaldistance may be considered substantially greater if the differencebetween the expansion portion of the stroke and a non-expansion portionof the stroke is either multiple times the width of the piston, thewidth of the piston, greater than three quarters the width of thepiston, greater than half the width of the piston, or greater than aquarter width of the piston. Thus, for example, a double-faced pistonmay have an axial length from one face of the piston to an opposite faceof the piston that is less than or equal to ½ of a distance from atleast one of the first cylinder head and the second cylinder head to anexhaust port.

In some embodiments, a cylinder and a piston may be sized such that thetotal distance the piston travels during each stroke from one end of thecylinder to the opposite end of the cylinder may exceed the distance thepiston travels during the expansion stroke portion of the stroke by atleast the length of the piston from one face to the opposite face. Inother exemplary embodiments, the cylinder and the piston may be sizedsuch that a total distance the piston travels in each stroke exceeds, byat least the length of the piston, a distance traveled by the pistonduring compression of gases on one side of the piston. The length ofpiston 50 from one face to the opposite face in an exemplary embodimentshown in the figures may be less than ½ of a distance from at least oneof cylinder heads 14, 15 to exhaust ports 18. This configuration andrelative sizing of the piston and cylinder may allow for a significantlygreater length of the total stroke for the piston in each directionduring which fresh pre-compressed air or other gases may be introducedinto the cylinder for the purposes of scavenging exhaust gases andcooling the cylinder after each combustion occurs at opposite ends ofthe cylinder.

In some embodiments, a cylinder and a piston may be configured such thatan amount of overshoot of the piston after the end of an expansion phasemay be substantially greater than the length of a compression volume.The compression volume may correspond to the clearance volume incylinder 12 as discussed above. For example, piston 50 and cylinder 12may be sized such that a length that piston 50 travels in a momentumstroke portion is substantially greater than the length of the clearancevolume between one side of piston 50 and the closest cylinder head 14,15 at the combustion position. In some embodiments, an amount ofovershoot is at least a quarter the length of piston 50. Setting anamount of overshoot in this manner to be, for example, at least aquarter the length of piston 50, may be useful to ensure a sufficientduration for scavenging to occur in cylinder 12.

In accordance with some embodiments of the present disclosure, aninternal combustion engine may include a piston kit being formed of anassembly of separate pieces, including a pair of piston rod portions anda piston comprising a disk. By way of example, and as shown in FIG. 4B,various embodiments of an engine according to the disclosure may includea double-faced piston, such as piston 50, and one or more piston rods,such as first piston rod portion 42 and second piston rod portion 43.Piston rod portions may extend from a center of the piston. For example,each of first piston rod portion 42 and second piston rod portion 43 mayextend from the radial center of piston 50. Piston 50, first piston rodportion 42, and second piston rod portion 43 may thus be coaxial.Because piston 50 moves linearly along axis A, and because mechanicalload may be transferred through second piston rod portion 43 that may beconnected to an actuator, load may be transferred along the same axis A.Thus, substantially all forces acting on piston 50 may act in adirection parallel to axis A. Furthermore, there are no side forcesacting on piston 50, i.e., forces acting in a direction perpendicular toaxis A. Compared to a conventional engine with pistons connected to acrankshaft, and which experience lateral forces, piston 50 may avoidside forces acting in a direction different from the primary movementdirection of the piston. Due to a lack of experiencing lateral forces,piston 50 may experience reduced stress and reduced accumulated heat,and thus, may have reduced need for cooling. In some embodiments, piston50 may be regarded as a transverse stressless action piston.Furthermore, piston kit 56 may be substantially rotationally symmetricabout axis A. Further still, in some embodiments, piston kit 56 may besymmetrical with respect to a median plane. The median plane may be aplane at an axial center of piston 50 that is perpendicular to axis A.

Engine 10 may be provided with a single air supply. The single airsupply may be connected to an inlet chamber. For example, in theembodiment as shown in FIGS. 5-14, inlet chamber 32 includes inletopening 29, which may be connected to a source that supplies air. Thesource that supplies air may be the only air supply provided in engine10. It is understood that inlet chamber 32 may be provided on the leftside of engine 10, as well. For example, the configuration of engine 10shown in FIGS. 5-14 may be mirrored. Air may be supplied to inletchamber 32 at a pressure that may be higher than atmospheric ambientpressure. When air is supplied in this manner, a design may be achievedthat is compact. Furthermore, such a design may be less complex than onerequiring separate air supplies.

When a single air supply is provided, inlet chamber 32 may be configuredto permit fresh air to flow into both first combustion chamber 71 andsecond combustion chamber 73. Furthermore, in some embodiments, firstvestibule 30 and second vestibule 31 may be configured as isolationareas. An isolation area may be an area external to cylinder 12 that isconfigured to isolate non-active piston rod parts during alternatecylinder charges. For example, first vestibule 30 may act as a firstisolation area on one side of cylinder 12 and second vestibule 31 mayact as a second isolation area on an opposite side of cylinder 12.

In some embodiments, multiple air supplies may be provided. For example,rather than providing inlet chamber 32, engine 10 may include two airsupplies, each configured to supply air to one of first vestibule 30 orsecond vestibule 31. Engine 10 may include a first air supply thatcommunicates with first vestibule 30 and a second air supply thatcommunicates with second vestibule 31, each through a respective sideopening 33. The two air supplies may be connected upstream of sideopenings 33. Thus, a single air supply may be bifurcated to formmultiple air supplies. In this embodiment, one or both of first pistonrod portion 42 and second piston rod portion 43 may include occludedends. In such cases, additional openings may be provided in first pistonrod portion 42 and second piston rod portion 43. For example, a furtherset of openings may be provided on first piston rod portion 42 that isspaced apart from first opening 44. The further set of openings may beconfigured to communicate gas from first vestibule 30 while firstopening is inside cylinder 12. The further set of openings may beconfigured to be outside cylinder 12 when first opening 44 is insidecylinder 12. A structure of the further set of opening may be similar tothat of first openings 44. Such further set of openings may be similarlyprovided in second piston rod portion 43.

Flow of gases within piston kit 56 may occur in different directions. Insome embodiments, a passageway in a piston assembly may be configured tocommunicate gas flow in a first direction from a first side of thepiston to a second side of the piston, and to communicate gas flow in asecond direction from the second side of the piston to the first side ofthe piston. For example, passageway 46 may be provided in piston rod 40,wherein passageway 46 is configured to allow gas flow in a firstdirection from area 67 on one side of piston 50 to the inside ofcylinder 12 through second opening 48. Piston 50 may be at the firstposition, for example at the combustion position on the right side ofcylinder 12 at the time of supplying gas to cylinder 12 through secondopening 48. Passageway 46 may also be configured to allow gas flow in asecond direction from area 65 on the opposite side of piston 50 to theinside of cylinder 12 through first opening 44. Piston 50 may be at thesecond position, for example at the combustion position on the left sideof cylinder 12 at the time of supplying gas to cylinder 12 through firstopening 44.

In some embodiments, flow of gases within piston kit 56 may be in thesame direction. For example, when inlet chamber 32 is provided, gas mayflow from inlet opening 29 through passageway 46 and into cylinder 12via second opening 48 (see FIG. 5). At another position of piston 50,gas may flow from inlet opening 29 through passageway 46 and intocylinder 12 via first opening 44 (see FIG. 10).

FIG. 15 illustrates an embodiment of engine 10 including chamber 39. Theembodiment of FIG. 15 may be similar to that of FIG. 5 except thatocclusion may be accomplished by chamber 39. Second piston rod portion43 may be provided without plug 49. Chamber 39 may be a structure thatis attached to or integral with second vestibule 31. Chamber 39 may besealed in an airtight manner. When piston 50 is in the second position,as shown in FIG. 15, air may be introduced from inlet opening 29.Because the left side of engine 10 is occluded, air that is inlet topiston rod 40 may travel through passageway 46 to area 67 but does notescape to areas outside engine 10. Instead, air may be forced intocylinder 12 through first opening 44. Thus, engine 10 may function in asimilar manner to that as shown in FIG. 5.

A piston rod may be configured such that the piston assembly is slidablebetween a position where piston rod openings are blocked and a positionwhere at least one of piston rod openings are opened. In some positionsthroughout the range of travel of piston 50, there may be positionswhere none of first opening 44 or second opening 48 is in fluidcommunication with cylinder 12. For example, FIGS. 6, 7, 8, 9, 11, 12,and 13 show instances where first opening 44 and second opening 48 havenot yet entered cylinder 12. A pressure buildup period may occurbetween, for example, the position of FIG. 6 and the position of FIG. 9.In a first pressure buildup position, such as that shown in FIG. 6,gases introduced from inlet opening 29 may be in fluid communicationwith passageway 46, but the gases may be unable to exit from engine 10.Thus, pressure may begin building in regions in fluid communication withinlet chamber 32, such as area 65, area 67, and inside passageway 46.Upon reaching a second pressure buildup position, such as that shown inFIG. 9, an internal pressure in regions in fluid communication withinlet chamber 32 may rise to a predetermined level. Thereafter, whenfirst opening 44 becomes exposed to the inside of cylinder 12, pressureis released and high-pressure air may be delivered to the inside ofcylinder 12. Delivery of high-pressure air into cylinder 12 may increasethe amount of work that engine 10 may output. For example, high-pressureair introduced into cylinder 12 may serve to further advance piston 50toward the left side of cylinder 12, as shown in the embodiment of FIG.9.

An engine in accordance with exemplary embodiments of the disclosure mayproduce further benefits. For example, an engine may facilitate nearlycontinuous scavenging of hot exhaust gases from the cylinder whilecontinuously supplying fresh air for combustion. The nearly continuouslyintroduced fresh pre-compressed air may decrease the temperature withinthe cylinder and increase the engine efficiency and engine service life.

Various alterations and modifications may be made to the disclosedexemplary embodiments without departing from the spirit or scope of thedisclosure. For example, the burned gases produced by the engine 10 maybe used for driving a turbo charger. The compressed air introduced intothe cylinder may be pressurized by an external compressor that is drivenby the reciprocating piston rod portions extending from opposite ends ofthe cylinder. Other variations may include imparting a swirl effect tothe gases introduced into the cylinder by changing the angle of theinlet ports and of the outlet ports so that gases are not directedradially into or out of the cylinder.

To expedite the foregoing portion of the disclosure, variouscombinations of elements are described together. It is to be understoodthat aspects of the disclosure in their broadest sense are not limitedto the particular combinations previously described. Rather, embodimentsof the invention, consistent with this disclosure, and as illustrated byway of example in the figures, may include one or more of the followinglisted features, either alone or in combination with any one or more ofthe following listed features, or in combination with the previouslydescribed features.

For example, there may be provided a linear reciprocating engine. Theengine may include a cylinder having a first combustion chamber at afirst end thereof and a second combustion chamber at an opposing secondend thereof; a first cylinder head located at an end of the firstcombustion chamber; a second cylinder head located at an end of thesecond combustion chamber; a piston slidably mounted within thecylinder; and a piston rod including at least one piston rod portionextending through the first combustion chamber and the second combustionchamber, the at least one piston rod portion having at least one firstport located on a first side of the piston and at least one second portlocated on a second side of the piston, opposite the first side of thepiston. There may also be provided the following elements:

-   -   wherein the at least one piston rod portion includes a        passageway extending through the piston configured to        communicate gas flow therethrough.    -   wherein the piston rod is slidable to a first position where the        at least one first port and the at least one second port are        blocked to enable a pressure build up in the passageway.    -   wherein the piston rod is slidable to a second position where        the at least one second port is open to release pressurized air        into the second combustion chamber.    -   wherein the piston rod is slidable to a third position where the        at least one first port is open to release pressurized air into        the first combustion chamber.

Furthermore, for example, there may be provided a linear reciprocatingengine including a cylinder having a first combustion chamber at a firstend thereof and a second combustion chamber at an opposing second endthereof; a vestibule located external to the first combustion chamberproximate the first end; a piston slidably mounted within the cylinder;a first piston rod portion extending from the piston through the firstcombustion chamber and into the vestibule, the first piston rod portionincluding a hollow tube portion having an inlet port and at least onefirst sidewall opening therein; and a second piston rod portionextending from the piston through the second combustion chamber, thesecond piston rod portion having a hollow tube portion and at least onesecond sidewall opening therein. There may also be provided thefollowing elements:

-   -   wherein the first piston rod portion is flow-connected to the        second piston rod portion.    -   wherein the at least one first sidewall opening and the at least        one second sidewall opening are positioned such that during a        first stroke portion, the at least one inlet port is located in        the vestibule to supply the first combustion chamber with air        from the vestibule.    -   wherein during a second stroke portion the at least one inlet        port is located in the vestibule to supply the second combustion        chamber with air from the vestibule.    -   wherein the engine further includes a fresh air pump connected        to the single air inlet.    -   wherein the engine further includes a pump for supplying        pressurized air to the vestibule.    -   wherein the engine includes two combustion chambers    -   wherein the single air inlet and piston rod are configured to        permit fresh air to flow into both combustion chambers.

Furthermore, for example, there may be provided a linear reciprocatingengine including a cylinder having a first combustion chamber at a firstend thereof and a second combustion chamber at an opposing second endthereof; a first vestibule located external to the first combustionchamber proximate the first end; a second vestibule located external tothe second combustion chamber proximate the second end; a pistonslidably mounted within the cylinder; a first piston rod portionextending from the piston through the first combustion chamber and intothe first vestibule, the first piston rod portion having a firstelongated passageway portion therethrough and at least one first porttherein; and a second piston rod portion extending from the pistonthrough the second combustion chamber and into the second vestibule, thesecond piston rod portion having a second elongated passageway portiontherethrough and at least one second port therein. There may also beprovided the following elements:

-   -   wherein the first passageway portion flow connects to the second        passageway portion.    -   wherein when the at least one first port is located in the first        vestibule, the at least one second port is located in the second        combustion chamber, thereby permitting flow communication        between the first vestibule and the second combustion chamber.    -   wherein when the at least one second port is located in the        second vestibule, the at least one first port is located in the        first combustion chamber, thereby permitting flow communication        between the second vestibule and the first combustion chamber.

Furthermore, for example, there may be provided an internal combustionengine including a cylinder having a first combustion chamber at a firstend thereof and a second combustion chamber at an opposing second endthereof; a vestibule external to the combustion chamber; a pistonslidably mounted within the cylinder; and a piston rod extending fromthe piston through the combustion chamber and into the vestibule. Theremay also be provided the following elements:

-   -   wherein the piston rod includes an opening therethrough        extending to the piston, and at least one port therein.    -   a port in the vestibule for supplying pressurized air to the        vestibule to thereby enable, during a combustion stroke of the        piston, pressurized air to move through the piston rod and cool        the piston.

Furthermore, for example, there may be provided a linear reciprocatingengine including a cylinder having a first combustion chamber at a firstend thereof and a second combustion chamber at an opposing second endthereof, the cylinder having one or more side ports therein; a firstcylinder head located at an end of the first combustion chamber; asecond cylinder head located at an end of the second combustion chamber;a double-faced piston slidably mounted within the cylinder; a firstpiston rod portion extending from the piston through the firstcombustion chamber and into a first pressurizable vestibule, the firstpiston rod portion having a first elongated passageway portiontherethrough and at least one first port therein; a second piston rodportion extending from the piston through the second combustion chamberand into a second pressurizable vestibule, the second piston rod portionhaving a second elongated passageway portion therethrough, the secondelongated passageway portion being flow connected to the first elongatedpassageway and at least one second port therein. There may also beprovided the following elements:

-   -   wherein the at least one first port and the at least one second        port are respectively arranged such that when the double-faced        piston is located in a central position in the combustion        chamber and the first vestibule and the second vestibule are        pressurized, a static air flow condition exists in the first        piston rod portion and the second piston rod portion.

1-20. (canceled)
 21. A linear reciprocating engine, comprising: acylinder having a first combustion chamber at a first end and a secondcombustion chamber at an opposing second end; a first cylinder headlocated at an end of the first combustion chamber; a second cylinderhead located at an end of the second combustion chamber; a pistonslidably mounted within the cylinder; and a piston rod including atleast one piston rod portion extending through the first combustionchamber and the second combustion chamber, the at least one piston rodportion having at least one first port located on a first side of thepiston and at least one second port located on a second side of thepiston, opposite the first side of the piston, wherein the at least onepiston rod portion includes a passageway configured to communicate gasflow therethrough, wherein the piston rod is slidable to a firstposition where the at least one first port and the at least one secondport are blocked to enable a pressure build up in the passageway,wherein the piston rod is slidable to a second position where the atleast one second port is open to release pressurized air into the secondcombustion chamber, and wherein the piston rod is slidable to a thirdposition where the at least one first port is open to releasepressurized air into the first combustion chamber.
 22. The engine ofclaim 21, wherein the passageway includes an interconnecting flowpassage extending through the piston.
 23. The engine of claim 21,wherein the at least one piston rod portion includes a first piston rodportion and a second piston rod portion, the first piston rod portionincluding the at least one first port, and the second piston rod portionincluding the at least one second port.
 24. The engine of claim 21,wherein the piston rod is connected at a center of the piston,symmetrically with respect to a longitudinal axis of the piston rod. 25.The engine of claim 21, wherein the piston rod is asymmetric withrespect to a median plane of the piston.
 26. The engine of claim 21,wherein the engine is provided with a single air supply.
 27. The engineof claim 21, further comprising: a first cylinder head located at an endof the first combustion chamber; a second cylinder head located at anend of the second combustion chamber, wherein the chamber is located onan a opposite side of the first cylinder head or the second cylinderhead.
 28. A linear reciprocating engine comprising: a cylinder having afirst combustion chamber at a first end and a second combustion chamberat an opposing second end; a vestibule located external to the firstcombustion chamber proximate the first end or the second end; a pistonslidably mounted within the cylinder; a first piston rod portionextending from the piston through the first combustion chamber and intothe vestibule, the first piston rod portion including a first passagewayflow-connected to an inlet port and at least one first sidewall opening;and a second piston rod portion extending from the piston through thesecond combustion chamber, the second piston rod portion including asecond passageway flow-connected to at least one second sidewallopening, wherein the first passageway is flow-connected to the secondpassageway.
 29. The engine of claim 28, further comprising: a firstisolation area on one side of the cylinder and a second isolation areaon an opposite side of the cylinder, wherein the first isolation areaand the second isolation area are configured to isolate non-activepiston rod parts during alternate cylinder charges.
 30. The engine ofclaim 28, wherein the at least one first sidewall opening and the atleast one second sidewall opening are positioned such that during afirst stroke portion, the at least one inlet port is located in thevestibule to supply the first combustion chamber with air from thevestibule.
 31. The engine of claim 30, wherein during a second strokeportion the at least one inlet port is located in the vestibule tosupply the second combustion chamber with air from the vestibule. 32.The engine of claim 28, wherein the engine includes a single air supplyconnected to the vestibule.
 33. The engine of claim 32, furthercomprising: a fresh air pump connected to the single air supply, whereinthe fresh air pump is configured to permit fresh air to flow into thefirst combustion chamber and the second combustion chamber.
 34. Theengine of claim 29, wherein the vestibule includes the first isolationarea or the second isolation area.
 35. The engine of claim 28, wherein:the piston is slidable to a first position where the at least one firstsidewall opening and the at least one second sidewall opening areblocked to enable a pressure build up in the first piston rod portionand the second piston rod portion, the piston is slidable to a secondposition where the at least one second sidewall opening is open torelease pressurized air into the second combustion chamber, and thepiston is slidable to a third position where the at least one firstsidewall opening is open to release pressurized air into the firstcombustion chamber.
 36. A linear reciprocating engine, comprising: acylinder having a first combustion chamber at a first end and a secondcombustion chamber at an opposing second end; a chamber located externalto the cylinder; a piston configured to be slidably mounted within thecylinder; a piston rod including a first piston rod portion and a secondpiston rod portion, wherein the first piston rod portion extends throughthe first combustion chamber and the second piston rod portion extendsthrough the second combustion chamber, and the first piston rod portionor the second piston rod portion extends into the chamber; at least onefirst opening in the first piston rod portion configured to move intoand out of the first combustion chamber to selectively communicate gasto the first combustion chamber; and at least one second opening in thesecond piston rod portion configured to move into and out of the secondcombustion chamber to selectively communicate gas to the secondcombustion chamber, wherein the piston rod is configured such that whenthe at least one first opening is outside the first combustion chamberand the at least one second opening is outside the second combustionchamber, pressure buildup occurs in the piston rod.
 37. The engine ofclaim 36, wherein the chamber includes a vestibule.
 38. The engine ofclaim 36, wherein the piston rod includes an interconnecting flowpassageway extending through the piston.
 39. The engine of claim 36,wherein the chamber is adjacent to the first combustion chamber or thesecond combustion chamber.
 40. The engine of claim 36, wherein thepiston rod is configured such that: when the at least one first openingis inside the first combustion chamber, pressurized air is released intothe first combustion chamber, and when the at least one second openingis inside the second combustion chamber, pressurized air is releasedinto the second combustion chamber.